Prospects for Detection of Exoplanet Magnetic Fields Through Bow-Shock Observations During Transits

TL;DR

This paper explores the potential for detecting exoplanet magnetic fields by observing asymmetries in transit light curves caused by bow shocks, classifying systems with observable shock signatures, and predicting specific asymmetries based on planetary and stellar magnetic interactions.

Contribution

It provides a classification of transiting systems based on their likelihood to produce observable bow-shock signatures and predicts light curve asymmetries linked to planetary magnetic fields.

Findings

36 out of 92 known systems may produce detectable shocks

Identified promising candidates like WASP-19b and CoRoT-11b

Predicted asymmetries can constrain planetary magnetic field strengths

Abstract

An asymmetry between the ingress and egress times was observed in the near-UV light curve of the transit planet WASP-12b. Such asymmetry led us to suggest that the early ingress in the UV light curve of WASP-12b, compared to the optical observations, is caused by a shock around the planet, and that shocks should be a common feature in transiting systems. Here, we classify all the transiting systems known to date according to their potential for producing shocks that could cause observable light curve asymmetries. We found that 36/92 of known transiting systems would lie above a reasonable detection threshold and that the most promising candidates to present shocks are: WASP-19b, WASP-4b, WASP-18b, CoRoT-7b, HAT-P-7b, CoRoT-1b, TrES-3, and WASP-5b. For prograde planets orbiting outside the co-rotation radius of fast rotating stars, the shock position, instead of being ahead of the planetary motion as in WASP-12b, trails the planet. In this case, we predict that the light curve of the planet should present a late-egress asymmetry. We show that CoRoT-11b is a potential candidate to host such a behind shock and show a late egress. If observed, these asymmetries can provide constraints on planetary magnetic fields. For instance, for a planet that has a magnetic field intensity similar to Jupiter's field (~ 14 G) orbiting a star whose magnetic field is between 1 and 100G, the stand-off distance between the shock and the planet, which we take to be the size of the planet's magnetosphere, ranges from 1 to 40 planetary radii.